6 28 fcom sa227 fuel

AIRCRAFT SYSTEMS

FUEL SA227‐ SERIES/FCOM/VTM 6.28.1 FUEL SYSTEM

The fuel system includes left and right integral wing fuel tanks with a total usable capacity of 648 U.S. gallons. Each wing tank contains an integral hopper tank that serves as a fuel sump for the boost pumps.

Two boost pump actuated jet transfer pumps are provided in each wing tank to maintain the hopper tanks at full capacity. With the jet transfer pumps operative, the usable full capacity per tank is 324 gallons (2,171 pounds at 6.7 pounds per gallon). The zero point on the fuel quantity gauge is adjusted to allow for 13.4 pounds (6 kg) of unusable fuel. With the transfer pump operative, the fuel quantity gauge readings represent the total usable fuel available in pounds. A crossflow valve provides for fuel balancing between tanks when required. An amber annunciator light illuminates when the fuel crossflow switch is placed in the OPEN position. The annunciator senses crossflow valve position and illuminates whenever the valve is not fully closed. See Figure 6.28‐1 for metric capacities.

FUEL STORAGE

Fuel for each engine is stored in two integral fuel tanks, one located in each wing. Each tank serves as an independent fuel system for its respective engine. The tanks are interconnected by a Crossflow line to balance the fuel quantity or to provide either engine with all of the fuel on board. Two gravity filled collector tanks in each wing tank, coupled with jet transfer pump action, supply a hopper tank with fuel, ensuring boost pump submergence in all flight attitudes. Two sump drain valves are located just outboard of wing stations 27, forward of the boost pump access panels. Another drain is located on the outboard side of each nacelle. The valves are used to drain accumulated water from the tank or may be used to drain residual fuel when defueling the tank. A flush‐mounted vent is located on the lower surface of the wing inboard of each wing tip. A vent balance line tees into the vent system and is routed along the entire length of the wing behind the rear spar.

REFUELING

NOTE

On a sloping ramp, the uphill tank may not accept a full fuel load if the downhill wing tank is filled first. When refueling on a sloping ramp, the uphill tank can be filled to maximum capacity by refilling both tanks simultaneously, by refilling the uphill wing tank first, or by adding fuel to the wings alternately in approximately 125 gallon (1042.5 lbs./ 470 litters) increments. When less than maximum capacity is required, this special fueling procedure is not necessary.

Revision: Original Aug 1,2013

GO/FCOM/SA227‐SERIES/VTM

AIRCRAFT SYSTEMS FUEL FUEL SYSTEM

SA227‐ SERIES/FCOM/VTM

6.28.2

Figure 6.28‐1

Revision: Original Aug 1,2013

GO/FCOM/SA227‐SERIES/VTM

AIRCRAFT SYSTEMS

FUEL SA227‐ SERIES/FCOM/VTM 6.28.3 JET TRANSFER PUMP SYSTEM

A schematic of the jet transfer pump system is shown in Figure 6.28‐2. The system is provided to transfer fuel from the collector tanks to the hopper tank in each wing. The hopper tank and two collector tanks (Forward & Aft) are at the most inboard section of each wing fuel tank. The hopper tank contains the boost pumps and feeds the engine driven fuel pump. The collector tanks gravity feed from the wing tank. Flapper valves prevent span wise flow of the fuel during maneuvering flight. Two jet transfer pumps are located in the dry center section inboard of the collector tanks and use boost pump flow to transfer fuel from the collector tanks to the hopper tank. The jet transfer pump system can fill the hopper tank 1.5 times as fast as the engine driven pump can drain it.

A flapper valve in the hopper tank allows fuel to gravity feed in from the wing tank. A float switch located in the hopper tank activates the respective amber XFER PUMP annunciator light whenever the fuel level in the hopper tank is below the equivalent of approximately 70 pounds. With the boost pumps off and fuel gravity feeding to the hopper tank, illumination occurs with about 600 to 700 pounds of fuel remaining in the wing tank. With the boost & transfer pumps operating and scavenging the collector tanks, the light will illuminate with approximately 70 pounds of usable fuel remaining (all of which would be in the hopper tank).

With the jet transfer system operating, the unusable fuel quantity is 2 gallons (13 pounds) per side. The fuel quantity indicating system is calibrated to exclude normally unusable fuel from the fuel gauge readings. However, without an operational jet transfer system, an additional 11 gallons (75 pounds) of unusable fuel would be trapped in the collector tanks and this unusable fuel would be shown on the fuel gauges.

During normal operation with the respective boost pump on, illumination of a L or R XFER PUMP annunciator light indicates that the jet transfer pumps are not maintaining the hopper tank at full capacity. Since the jet transfer pumps operate due to boost pump flow, the first action when a XFER PUMP caution light illuminates is to select the other boost pump for that tank. If that does not extinguish the light, the transfer pump system can be assumed to be inoperative and the unusable fuel in that tank would be increased 75 pounds.

The XFER PUMP annunciator light will be illuminated with less than 600 to 700 pounds of fuel per wing tank with boost pumps off, and with less than 65 to 75 pounds of fuel per hopper tank with boost pumps on. When the caution light illuminates with less than 70 pounds of fuel available, at landing should be made as soon as practicable or, if fuel is available in the opposite tank, the cross flow valve should be opened.

Revision: Original Aug 1,2013

GO/FCOM/SA227‐SERIES/VTM

AIRCRAFT SYSTEMS FUEL JET TRANSFER PUMP SYSTEM

SA227‐ SERIES/FCOM/VTM

6.28.4

Figure 6.28‐2

Revision: Original Aug 1,2013

GO/FCOM/SA227‐SERIES/VTM

AIRCRAFT SYSTEMS

FUEL SA227‐ SERIES/FCOM/VTM 6.28.5 BOOST PUMPS

Two submerged boost pumps are installed in the hopper tank of each wing. The pumps are connected through check valves to a common supply line. See Figure 6.28‐3. Excess boost pump flow is tapped off the supply line for use in the jet transfer pump system. A fuel shutoff valve installed in each nacelle can be used to stop fuel flow to the engine. A fuel pressure transmitter senses interstage pressure of the engine driven fuel pump. When the engine is not operating, the fuel pressure gauge will indicate boost pump pressure. After the engine is operating the fuel pressure displayed will be a combination of engine driven pump pressure and boost pump pressure.

Each essential bus provides power for one pump, in each wing (i.e. L ess bus powers L Main & R Aux boost pumps). This is a safety feature should either bus be inoperative. The two pumps within each wing are designated main and auxiliary. These designations are for purposes of identification only as the pumps are identical. Two three‐position switches (MAIN‐OFF‐AUX) are installed in the center pedestal, one for each pair of pumps.

Figure 6.28‐3

FUEL SHUTOFF VALVE

A lever lock toggle switch on the center pedestal in the cockpit controls a fuel shutoff valve for each engine. The shutoff valve is located in the upper left hand corner of the wheelwell along the left hand keelson and the main wing spar.

The shutoff valve is motor operated and controlled by the two position (OPEN‐CLOSED) toggle switch.

Limit switches are incorporated in the valve to de‐energize the motor when the gate reaches the full open or closed position. The position of the valve is annunciated on a sub‐annunciator panel when the valve has not reached its intended position.

Revision: Original Aug 1,2013

GO/FCOM/SA227‐SERIES/VTM

AIRCRAFT SYSTEMS

FUEL SA227‐ SERIES/FCOM/VTM 6.28.6 FUEL CROSSFLOW

The fuel crossflow system provides the capability of maintaining proper fuel balance between integral wing tanks. The system consists of a two inch line that interconnects the wing tanks, a Crossflow valve for permitting fuel flow between the tanks, and a fuel drain for quick defueling of the aircraft. The crossflow line is located in the center section aft of the main wing spar and is accessible through panels in the wing center section. The motor actuated crossflow valve is controlled by a combination light and switch located on the instrument panel. The light illuminates when the switch is actuated to open the valve and remains on until the switch is reactuated to the closed position. In addition, crossflow valve position is annunciated by a light on the sub‐annunciator panel. This light illuminates whenever the valve is not in its closed position.

Figure 6.28‐4

Revision: Original Aug 1,2013

GO/FCOM/SA227‐SERIES/VTM

AIRCRAFT SYSTEMS

FUEL SA227‐ SERIES/FCOM/VTM 6.28.7 FUEL QUANTITY SYSTEM

The fuel quantity system is comprised of two capacitance fuel gauge systems, one for each integral wing tank. Each system includes five tank sensors, and a low level caution light (XFER PUMP) on the annunciator panel. The fuel quantity system uses the difference in capacitance between fuel and air to measure the amount of fuel in the tanks. As the tank is filled, more of the probes are covered by fuel with a resultant change in capacitance. The dual indicator, which houses a bridge circuit, an amplifier, and servo motor, converts the tank sensor capacitance into a dial presentation of measured fuel quantity in hundreds of pounds. The low level caution light is activated by a float switch in each hopper tank.

Since the density (and therefore weight) of the fuel changes with temperature, the fuel quantity system, without compensation, would only be accurate in a narrow temperature range. To prevent this occurrence, the most inboard fuel probe has a temperature sensitive compensator section. The output of the compensator is used by the indicator to provide an accurate display of fuel weight regardless of temperature. A push‐to‐test button near the quantity indicator is used to test each system. When the button is depressed, the indicator needles should move to the 12 o’clock position. When the button is released, the needle should return to the correct fuel quantity indication. This procedure tests all the electrical and mechanical functions within the indicator.

Figure 6.28‐5

Revision: Original Aug 1,2013

GO/FCOM/SA227‐SERIES/VTM

AIRCRAFT SYSTEMS

FUEL SA227‐ SERIES/FCOM/VTM 6.28.8 MAGNA‐STICKS

Magna‐sticks are optional, direct‐reading, mechanical fuel level indicators. One is mounted on the fuel cell access plate on the bottom of the wing, just inboard of each nacelle. They provide visual indications of the usable fuel quantity in the respective tank if the tank contains between approximately 30 and 155 U.S. gallons. A doughnut shaped float is free to slide up and down a fixed tube and draw with it a calibrated indicator stick to show the level of fuel in the tank. The indicator stick is normally held fixed inside the tube by locking tabs at the base of the stick. A quarter turn of the base unlocks the stick and allows it to drop down to its indicating position.

Magnets draw the indicator stick to the level of the float when the stick is unlocked. The indicator stick is graduated to show fuel quantity in U.S. gallons. The internal geometry of the fuel tank and the dihedral of the wing affect the spacing of the quantity marks on the stick and limit the useful range of this indicating system. With less than approximately 25 gallons in the tank, the float may rest on structure inside the tank. With more than approximately 160 gallons aboard, the float will be at the top of the tube and no longer floating on top of the fuel. Therefore, Magna‐sticks are useful when fuel tanks are less than half full but have at least 30 gallons in them.

Accurate readings are obtainable only when the airplane is on a reasonably level ramp because the Magna‐stick indications depend upon the level of the fuel in the tank. Avoid inaccurate readings caused by binding of the indicator stick in its bushing by tapping the bottom surface of the wing around the Magna‐stick housing before taking readings. Accurate determination of usable fuel in a tank (within plus or minus two gallons) is obtained by using the plane of the bottom surface of the wing and access plate to read the graduations on the indicator stick.

Figure 6.28‐6

Revision: Original Aug 1,2013

GO/FCOM/SA227‐SERIES/VTM